Brain injuries, including brain diseases, are a major health problem both in the US and worldwide. Many brain injuries arise from hypoxia, including focal hypoxias, often caused by stenosis or blockage in the blood supply to the brain, and diffuse hypoxias, generally caused by constrictions in a subject's air supply. Focal hypoxias can lead to, for instance, cortical infarcts and stroke. Diffuse hypoxias can lead to hypoxic ischemic brain injury (“HI injury”). Cortical infarcts and stroke, as well as HI injury, are significant health concerns.
HI injury and its related outcomes affect a significant number of live births every year. Measuring the incidence and effects of ischemic and hypoxic brain injury in children is complex; but, the number of patients affected is large by any assessment. HI injury has an incidence as high as 1 in 4000 live births. See Nelson et al. Lancet Neurol. 3:150-158 (2004). Most of these infants survive with considerable cognitive and motor deficits. See Barker, Ann Med. 31: Suppl 1:3-6 (1999). Neonatal encephalopathy due to all causes occurs in 1 to 6 of every 1000 births. See, for instance, the American College of Obstetricians and Gynecologists website: www.acog.org. The risk of intrapartum neonatal asphyxia is estimated at 2.5% of all live births. See Heinonen et al., BJOG 109: 261-264 (2002). Out of this large number of infants, a lesser number experience HI encephalopathy significant enough to produce brain injury with associated motor and cognitive disability. Cerebral palsy, or chronic, non-progressive motor disability, affects 1 to 2 per 1000 individuals in the United States. About 6% of these patients have acquired their disability through birth injuries related to HI injury. See, for instance, the NINDS website at www.ninds.nih.gov.
The current overall clinical outcome of term infants with HI injury is poor. Of all term neonates that suffer a HI injury, 10% die and 30% are permanently neurologically impaired. See Volpe, NEUROLOGY OF THE NEWBORN, 4th Ed., W.B. Saunders, Philadelphia (2001). Statistics generated from the control group of the recently published Phase I hypothermia trial, Randomized Controlled Trial of Hypothermia for Hypoxic-Ischemic Encephalopathy in Term Infants, found even higher levels of mortality: 37% of included neonates died and 25% were neurologically impaired. See Shankaran et al., N Engl J Med. 353: 1574-1584 (2005).
Other than supportive care, therapy for HI injury is limited. Whole body hypothermia has been reported as safe and beneficial in a multicenter Phase I clinical trial in treatment of neonatal HI. However, the usefulness of the therapy appears limited to the period shortly after birth. See Shankaran (2005) cited above.
The lack of therapy, number of affected individuals, coupled with the costs necessary to facilitate care and rehabilitation for life, indicate that HI injury represents a current, significant, unmet medical need. Much the same applies to a variety of other conditions characterized by damage to brain tissue, particularly cortical brain tissue, such as that resulting from hypoxia, infarction, and other injuries and/or insults, such as, for example injuries that produce ischemia and/or necrosis, such as ischemia and/or necrosis resulting in and/or associated with HI brain injury, cerebral accident, and/or stroke. There is therefore a need for improved methods for the treatment of these and related and similar injuries, pathologies, and diseases.
The use of stem cells has attracted some interest for this purpose, and there have been some encouraging observations in this area. A variety of stem cells have been isolated and characterized in recent years. They range from those of highly restricted differentiation potential and limited ability to grow in culture to those with apparently unrestricted differentiation potential and unlimited ability to grow in culture. The former have generally been the easier to derive and can be obtained from a variety of adult tissues. The latter have had to be derived from germ cells and embryos, and are called embryonal stem (“ES”) cells, embryonal germ (“EG”) cells, and germ cells. The embryonal stem (“ES”) cell has unlimited self-renewal and can differentiate into all tissue types. ES cells are derived from the inner cell mass of the blastocyst. Embryonal germ (“EG”) cells are derived from primordial germ cells of a post-implantation embryo. Stem cells derived from adult tissue have been of limited value because they are immunogenic, have limited differentiation potential, and have limited ability to propagate in culture. ES, EG, and germ cells do not suffer from these disadvantages, but they have a marked propensity to form teratomas in allogeneic hosts, raising due concern for their use in medical treatments. For this reason, there is pessimism about their utility in clinical applications, despite their advantageously broad differentiation potential. Stem cells derived from embryos also are subject to ethical controversies that may impede their use in treating disease.
Some efforts to find an alternative to ES, EG, and germ cells have focused on cells derived from adult tissue. While adult stem cells have been identified in most tissues of mammals, their differentiation potential is restricted and considerably more narrow than that of ES, EG, and germ cells. Indeed many such cells can give rise only to one or a few differentiated cell types, and many others are restricted to a single embryonic lineage. For instance, hematopoietic stem cells can differentiate only to form cells of the hematopoietic lineage, neural stem cells differentiate into cells only of neuroectodermal origin, and mesenchymal stem cells (“MSCs”) are limited to cells of mesenchymal origin (mesodermal cell types). Accordingly, these types of stem cells are, inherently, limited in their therapeutic applicability.
Accordingly, there has been a need for stem cells that can be used for treatment of cortical infarcts, HI injury, and other diseases that have the self-renewing and differentiation capacity of ES, EG, and germ cells but are not immunogenic; do not form teratomas when allografted or xenografted to a host; do not pose other safety issues associated with ES, EG, and germ cells; retain the other advantages of ES, EG, and germ cells; are easy to isolate from readily available sources, such as placenta, umbilical cord, umbilical cord blood, blood, and bone marrow; can be stored safely for extended periods; can be obtained easily and without risk to volunteers, donors or patients, and others giving consent; and do not entail the technical and logistical difficulties involved in obtaining and working with ES, EG, and germ cells.
A type of cell, called herein multipotent adult progenitor cells (“MAPCs”), has been isolated and characterized (see, for instance, U.S. Pat. No. 7,015,037, which is herein incorporated by reference in its entirety). (“MAPCs” also have been referred to as “MASCs.”) These cells provide many of the advantages of ES, EG, and germ cells without many of their drawbacks. For example, MAPCs are capable of indefinite culture without loss of their differentiation potential. They show efficient, long term engraftment and differentiation along multiple developmental lineages in NOD-SCID mice and do so without evidence of teratoma formation (often seen with ES, EG, and germ cells) (Reyes, M. and C. M. Verfaillie Ann NY Acad Sci. 938: 231-5 (2001)).